Method of forming precast concrete structural components



1 O6 9 7 CROSS REFERENCE EXAMINER July 9, 1969 c. 1.. SAINTY 3,458,510

METHOD OF FORMING PRBCAST CONCRETE STRUCTURAL COMPONENTS FiledDec. 21.1965 FIG FIG 2 2 I 0 a j j j 1 l L I l I HGJL H6 4 United States Patent3,458,610 METHOD OF FORMING PRECAST CONCRETE STRUCTURAL COMPONENTSChristopher Lawrence Sainty, Hassocks, England, assignor to StructuralConcrete Components Limited, Hassocks, England, a British company FiledDec. 21, 1965, Ser. No. 515,328 Claims priority, application GreatBritain, Dec. 22, 1964, 51,985/ 64 Int. Cl. B28b 1/08 US. Cl. 264-69 2Claims ABSTRACT OF THE DISCLOSURE In manufacturing lightweight precastconcrete structural components having two predominant densities, a stiffmix of appropriate viscosity of spherical aggregate of substantiallyuniform size and a matrix material consisting of fine gritty material,cement and water is formed. The proportions of the spherical aggregateand the matrix material in the stiff mix are such that the total volumeof the matrix material is substantially less than the volume of voidsbetween the spherical aggregate when measured alone. The mix is thenplaced in a mold and vibrated so as to distribute the matrix to coat allof the spherical aggregate and to fill the voids in the lower portion ofthe mold thereby forming a structural component having a solid lowerportion and a porous upper portion. The component is then removed fromthe mold and can be used.

The invention relates to a method for forming precast concretestructural components, particularly but not exclusively to precast floorbeams and slabs, while the object of the invention is to provide amethod for forming precast floor beams and slabs which are light inweight in comparison with their strength.

It is common knowledge that in a simple reinforced concrete beamdesigned to be subjected to loads acting vertically downwards, theconcrete above the neutral axis is subjected to compressive forces,which forces the concrete is suitable to resist, and that below theneutral axis the beam is subjected to tensional forces which concretealone is not suitable to resist and that steel reinforcement is providedto resist the tensional forces.

It is known to provide reinforced concrete beams in which the crosssection area of the concrete below the neutral axis is substantiallyless than the area of concrete above the neutral axis, the concretebeing of the same consistency throughout, thereby to economize in thevol ume of concrete used and to reduce the weight of the beams withoutsubstantially affecting the strength of the beams.

It is now proposed in accordance with the present invention to produceprecast concrete beams, slabs and other structural components in whichthe density of the concrete is different in different parts of thecomponents, that par of the component being subjected under load tocompressive forces being of dense concrete while the parts not sosubjected are of a less dense nature.

It is proposed in accordance with the invention to make use of aparticular property of uniform spherical aggregate. Such aggregatecan-be natural, but is rarely found sufiiciently spherical and uniformin shape, and it is there fore preferred to use a manufactured sphericalaggregate such as pellets of clay, shale or like argillaceous materialswhich have been rendered spherical and baked, such as known by the nameArgilag" R.T.M.

If a stiff mix of appropriate viscosity is made with a uniform sphericalaggregate of substantially uniform size,

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a fine gritty material, such for example as sand, fiy ash or crushednatural or manufactured mineral material, cement and water, in which thetotal volume of the matrix is less than that of the voids in theaggregate measured alone, it is possible to vibrate the mix in he mouldfor the structural component so that the lower part becomes solid whilethe upper part becomes porous. If the component is a floor beam thesolid part is required above the neutral axis and therefore the beam ismoulded upsidedown.

With aggregates of the type mentioned, and with vibration of suitableamplitude, frequency and duration, it is possible to produce concretecomponents with the desired proportion of solid and porous parts,depending upon the ratio of the quantity of matrix used to the quantityrequired to completely fill all the voids in the aggregate. Concrete ofthis sort can be made with very high com-pressive strength in the solidpart and very much lower strength, modulus of elasticity and weight inthe porous part.

The technique proposed above presents no difficulties in the manufactureof'concrete components on a large scale.

The invention consists in a method of manufacture of precast concretestructural components such as floor beams and slabs, comprisingpreparing a stiff mix of appropriate viscosity of spherical aggregate ofsubstantially uniform size, fine gritty material, cement and water insuch proportions that the total volume of the matrix is substantiallyless than the volume of the voids in the aggregate when measured alone,placing the mix in a mould of the shape of the component to bemanufactured, vibrating the mix in the mould at a suitable amplitude,frequency and duration as will distribute the matrix in the requiredlocation within the interstices in the aggregate under the action ofgravity.

The invention further consists in a method of manufacture of precastconcrete structural components as set forth in the preceding paragraphin which the vibration of the mix is carried out for such duration thatthe concrete at the bottom of the mould is dense and without voids whilethe concrete at the top of the mould is porous.

In one method of manufacture in accordance with the invention it isproposed to cast beams in moulds with a smooth fiat bottom plate, withthe main reinforcement secured in the upper part of the mould. There maybe provided in the lower part of the mould light reinforcement solelyfor the purpose of making the beams safe against breakage in handling.When the beams are finished the lower part in the mould is the densepart and the beams are therefore installed with this part uppermost, sothat it forms the compressive zone above the neutral axis.

The accompanying drawing shows diagrammatically, by way of example only,the precast aggregate component in the course of manufacture in which,

FIGURE 1 is a cross section through a mould filled with the mix beforeit is vibrated,

FIGURE 2 is a cross section of the same mould after the mix has beenvibrated,

FIGURE 3 is an enlarged part-section showing the relationship betweenthe aggregate, and the cement before it is vibrated, while,

FIGURE 4 is an enlarged part section showing the relationship betweenthe aggregate of the cement after the mix has been vibrated.

The mould shown in FIGURES 1 and 2 has side wall portions 1 and 2 whichstand upon a flat bottom plate 3, while the main reinforcement parts 4are secured in position as shown, by any known convenient method. At thesame time that the mix is placed in the mould, the solid matter and thevoids will be distributed in random manner throughout the mould asrepresented by the cross hatching of average density,

After the mix has been vibrated at a suitable. amplitude and frequency,and for a suitable duration, the mix will sink in the mould and allvoids in the lower part of the mould will be filled and only that parttowards the upper part of the mould will contain voids, as shown in FIG-URE 2 and represented by the dense and light cross hatchingrespectively.

During the process of mixing the concrete all the spherical aggregate iswetted by the cement and when first placed in the mould a superfluity ofthe cement and sand is positioned in places such as indicated at 5 inFIGURE 3 while the spherical aggregate in other places such as at 6 isin contact and has a thin coating all over with additional cement aroundthe points of contact, held there by surface tension.

When the mould has been fully vibrated the excess cement falls to thebottom of the mould and fills the voids as at 7 up to a predeterminedlevel, while above this level the whole of the concrete is provided withvoids.

The main function of the porous part of the beam is to support andlocate the main reinforcement. Depending upon the duty the beam has toperform the solid part might generally constitute one fifth or less ofthe total depth of the beam.

One advantage of manufacturing beams in the proposed manner is that theycan be supplied to the building site and be laid to form a floor with asmooth and fiat upper surface and thus avoid the necessity of laying ascreeding thereon. Floor beams may be about twelve inches wide andlittle difiiculty is experienced in laying them side by side to providea level, smooth surface over any required area and where the jointsbetween the beams are filled with a suitable cement and sand mix.

The edges of the beams in the porous area may be so shaped that, whenforced together, a concentrated load on one beam may be transferred tothe adjacent beam.

If desired the beams may be made of such sections that channels are leftin the upper surface of the fioor between adjacent beams for theaccommodation of electric conduits and the like, and since the concreteforming the lower layers of the floor is comparatively soft, holes maybe punched through where necessary for electrical outlets.

The tensile strength of the porous part of the component may beincreased by the addition of fibrous material of a mineral character tothe mix or a binding emulsion may be added to the cement if desired toincrease its tensile strength.

It is also within the scope of the invention to manuiacture panels whichmay be used as wall panels having an external solid face which isimpermeable while the inner porous face provides insulation against heatloss. Such panels can be substituted with advantage for cavity walls andthe external face can be provided with any desired finish.

Only beams, slabs and panels have been referred to hereinbefore, but itis to be understood that precast concrete components of other forms maybe constructed in accordance with the present invention.

I claim:

1. A method of manufacturing lightweight precast concrete structuralcomponents such as beams and slabs comprising the steps of introducingspherical aggregate of substantially uniform size and matrix materialconsisting of fine gritty material, cement and water to form a stiffmix, said mix having proportions of said spherical aggregate and saidmatrix material such that the total volume of said matrix material issubstantially less than the volume of voids between said sphericalaggregate when measured alone; placing said stilf mix in a mold definingthe particular structural component being cast; vibrating said stiff mixin said mold at a predetermined amplitude, frequency and duration aswill distribute said matrix to coat all of said spherical aggregate,uniformly distribute said spherical aggregate in said mold, and fill inthe voids between said distributed spherical aggregate in the lowerportion of said mold thereby forming a solid lower portion and a porousupper portion; and removing the so formed structural component from saidmold.

2. A method of manufacture as claimed in claim 1 in which said sphericalaggregate is of the manufactured kind.

References Cited Troxell and Davis, Concrete, 1956, page 97. Orchard, D.F., Concrete Technology, volume 2, 1962, pp. 230-231.

ROBERT F. WHITE, Primary Examiner I. H. SILBAUGH, Assistant Examiner US.Cl. X.R. 106-97; 26471

